1. Technical Field
The invention relates generally to bathyphotometers, and, in particular, to a vertical profiler for measuring stimulated bioluminescence.
2. Background Information
The need for direct measurements of oceanic plankton distribution has lead to the development of optical instrumentation designed to provide data which can be correlated with organism distribution patterns. Such instruments as the beam transmissometer and fluorometer have gained widespread use and with appropriate calibrations allow direct intercomparison of results collected by different investigators. Bathyphotometers designed to measure light from the large number of planktonic organisms which are bioluminescent, have not achieved similar status, although bioluminescence has been promoted as a highly specific bio-optical assay. Lack of comparability in sampling efficiency and differences in bioluminescence excitation and measurement among bathyphotometer designs has been a serious detriment to the general utility of bioluminescence measurements.
There are two types of bathyphotometers: those which measure unstimulated or spontaneous bioluminescence and, more commonly, those designed to measure stimulated bioluminescence. The latter have the greatest potential utility for rapid vertical profiling of the water column and a large number of different designs have been employed for this purpose. One design has been an open field detector which depends on movement of the instrument through the water to stimulate bioluminescence. Stimulation has also been achieved using a disc equipped with "brushes" rotating in open water at a fixed orientation to a detector. Detectors viewing an enclosed volume may depend on movement of the detector through the water to generate turbulence, but usually a pump is used to draw water through the detection chamber and turbulence is generated by an impeller or constriction. For example, a paper by J. Aiken and J. Kelly entitled A Solid State Sensor for Mapping and Profiling Stimulated Bioluminescence in the Marine Environment, published in CONTINENTAL SHELF RESEARCH, Vol. 3, No. 4., pp. 455-464, 1984, describes a towed bathyphotometer having a 2.6 cm inlet diameter and a detector dwell time of 25 milliseconds at the maximum flow rate of 1.5 liters per second, with excitation of bioluminescent organisms being produced partly by undefined turbulence and partly by a turbine flowmeter.
In the past, oceanography scientific researchers have utilized small intake pumped bathyphotometers with various types of uncalibrated mechanical stimulation of light. The maximum flow rates of these known bathyphotometers did not exceed 1.5 liters per second, which was not considered statistically significant. Thus, instruments were typically held at various depths for relatively long periods of time, up to 30 minutes, in attempts to quantify the stimulated light. In addition, these sensors were initially designed for near coastal phytoplankton work and almost completely missed the equally prominent offshore zooplankton population. Data from various bathyphotometers have been difficult to correlate to each other and to any standards because of their varied and low pumping rates as well as their various excitation mechanisms and detector dwell times.